This invention relates to functionalized polymers and to a method of preparing such polymers. More particularly, this invention relates to hydrogenated polymers containing functional groups and to a method for preparing such polymers.
Polymers containing ethylenic unsaturation are, of course, well known in the prior art. When these polymers are prepared by the addition polymerization of a polyunsaturated olefin, the unsaturation may be contained within the polymer backbone or pendent therefrom dependent upon the addition mechanism. For example, when 1,3-butadiene is the monomer, the unsaturation will be internal when the addition is 1,4 and external when the addition is 1,2. As is also known in the prior art, both of these unsaturations are relatively unstable and are subject to both thermal and oxidative degradation. In a diolefin homopolymer or a random copolymer, degradation of an internal double bond simply reduces the average molecular weight of the product. When such degradation occurs in a block copolymer, however, degradation of an internal double bond may be far more serious even to the extent of destroying desired polymeric properties. Degradation of an external unsaturation, on the other hand, in all such polymers simply reduces the polymers elastomeric properties. It is, of course, well known in the prior art to hydrogenate addition polymers containing both internal and pendent unsaturation to avoid such degradation. Hydrogenation of such polymers is taught, for example, in U.S. Pat. Nos. 3,419,365; 3,644,588; 4,400,478; 4,578,429 and Re. 27,145.
The incorporation of one or more functional groups into a polymer containing unsaturation to improve its properties for various uses is also well known in the prior art. Methods for incorporating functional groups into such polymers are taught, for example, in U.S. Pat. Nos. 3,135,716; 3,150,209 and 4,409,357. When the ethylenic unsaturation in the initial polymer is completely saturated via hydrogenation however, it has not, heretofore, been possible to incorporate functional groups into the polymer via these techniques. Moreover, when the starting polymer is a copolymer of a vinyl aromatic hydrocarbon and a polyolefin, and the residual unsaturation initially in the polyolefin portion of the copolymer has been substantially completely saturated via hydrogenation, the functional groups will be incorporated exclusively into the aromatic portion of the copolymer. Functional groups incorporated into the aromatic portion of the copolymer may not, however, be as reactive as those incorporated into the polyolefin portion of the copolymer. Moreover, functional groups incorporated into the aromatic portion of a copolymer may not, in all cases, result in the same end-use properties.
While it is, at least, theoretically possible to first incorporate one or more functional groups into a polymer and then to hydrogenate the functionalized polymer, attempts to do this have not been successful to date primarily due to poisoning of the hydrogenation catalyst by the functional group. Attempts to accomplish such hydrogenation have also been hampered by the potential for reductive hydrogenation and by conversion of the functional group during hydrogenation.
As indicated supra, it is also, theoretically, possible to first hydrogenate the polymer product and to then metalate the hydrogenated product to facilitate functionalization of the hydrogenated polymer. Metalization of a hydrogenated copolymer of a conjugated diene and a monovinylarene is taught in U.S. Patent No. 4,145,298. According to the disclosure of this patent, however, the metalated sites are then used to graft organic nitrogen compounds so as to produce a viscosity index improver. To the extent that the residual unsaturation in the diolefin portion of the polymer is substantially completely hydrogenated, however, the metal sites will be incorporated principally, if not exclusively, in the aromatic portion of the polymer. Such metalization, i.e., in the aromatic portion of the polymer generally requires the use of more metalating agent than does metalization of residual unsaturation in the diolefin portion of the polymer and, generally, requires the use of one or more metalization promoters such as an amine. Moreover, hydrogenation followed by metalization increases the number of steps required to accomplish the end result.
In light of the foregoing, it is clear that it has, heretofore, not been possible to produce a functionalized hydrogenated copolymer of a monoalkenyl aromatic hydrocarbon and a polyolefin wherein the functional groups are predominantly in the polyolefin portion of the polymer, at least not when the functional groups are two or more carbon atoms removed from any residual unsaturation. Moreover, it has not, heretofore, been possible to produce a functionalized, hydrogenated polymer without accomplishing each in a distinctly separate step. The need, then, for a functionalized, hydrogenated copolymer of a monoalkenyl aromatic hydrocarbon and a polyolefin wherein the functional groups are at least predominantly in the polyolefin portion of the copolymer and the need for a process wherein such a copolymer may be prepared with a reduced number of steps is believed to be readily apparent.